Technical Abstract:
Lack of a means to include snowmelt runoff and erosion in the Revised Universal Soil Loss Equation Version 2 (RUSLE2) hampers its use in areas where there is erosion due to melting of snow accumulated during the winter. Performance of other models that use RUSLE2 as the driver for hill slope erosion is also affected. Because RUSLE2 relies on externally-calculated, down-loaded data sets to drive the erosion process, we sought a model that could effectively estimate daily snow accumulation and melt. Snowmelt erosivity databases could then be developed using long-term daily disaggregated weather data from PRISM-based RUSLE2 climate databases. The Soil-Plant-Air-Water (SPAW) model was selected and tested for ability to simulate accumulation and melt of snow. Tests were based on daily weather data collected over a thirty to forty-one-year period from selected weather stations in cold or high elevation cropland areas of the western US, the northern Great Plains, the upper Midwest and the north-eastern US. Depth of new snow predicted with SPAW using default parameters was generally less than observed and the snow pack was predicted to melt before observed records indicate. Adjusting the accumulation and melt temperatures allowed for a better match to the observed data. The RUSLE2 daily disaggregated weather data were then used in SPAW to develop daily snow water equivalent accumulation and melt values for the selected locations. For most cold or heavy snow areas, reasonable estimates of timing of the accumulation and melt of snow can be obtained using the SPAW model with the daily temperature and precipitation values in RUSLE2 databases. By totaling daily snowmelt and rainfall erosivity values, this approach will allow development of RUSLE2 erosivity databases that will estimate both snowmelt and rainfall-caused erosion.